This invention relates to a method and apparatus for measuring traffic flows or in other words, the flows of vehicles, inside and near a crossing.
The present invention relates also to a technique which utilizes the result of measurement obtained by the invention for the structural design of crossings, such as signal control, disposition of right turn-only signal, a right turn lane, a left turn preferential lane, and so forth.
Conventional traffic flow measurement has been carried out by disposing a camera above a signal light taking the images of vehicles flowing into a crossing at the time of a green signal by one camera and measuring the number and speeds of the vehicles as described, for example, in "Sumitomo Denki", Vol. 130 (Mar. 1987), pp. 26-32. In this instance, a diagonal measurement range is set to extend along right and left turn lanes and brightness data of measurement sample points inside the measurement range are processed in various ways so as to measure the number and speeds of the vehicles.
However, the conventional system described above does not take sufficiently into consideration the overlap of vehicles and is not free from the problem that extraction and tracking of vehicles cannot be made sufficiently because smaller vehicles running beside larger vehicles are hidden by the latter and larger vehicles which are turning right, or about to turn right, hide opposed smaller vehicles which are also turning right.
The prior art system has another problem that the traffic flow cannot be accurately determined at a transition from yellow light to red light because the system checks only the vehicles entering the crossing at the green light.